Difference for SO2 and CO2 in TGML ionic liquids: a theoretical investigation

Abstract

Quantum chemical calculations (QM) have been used to investigate the interaction between sulfur dioxide (SO₂) or carbon dioxide (CO₂) molecules and ions of 1,1,3,3-tetramethylguanidium (TMG) lactate (LAC) (TMGL) ionic liquid. The QM results give us a deeper understanding of the factors that govern the high solubility of SO₂ in TMGL and the difference in the solubility of SO₂ and CO₂ in TMGL. The predicted geometries and binding energies imply a strong organization of SO₂ about the TMGL components, especially the LAC anion; but indicate a relatively weak organization of CO₂. Both the SO₂ and CO₂ molecules can interact with the TMG cations forming a N–H⋯O interaction; however, the binding energies demonstrate that the interaction with CO₂ is weaker than that with SO₂. The theoretical results indicate that the oxygen atoms of the LAC anion are the main active sites for the absorption of SO₂. Strong S⋯O interactions are found for both the SO₂–LAC and SO₂–TMGL complexes.